I thought about it too at first. But look at the callsites, all butone of them do not even expect this function to return NULL, so ifthis condition had ever been true, we would have seen crashes in thecallsites.

The only caller that checks for NULL ismem_cgroup_get_reclaim_stat_from_page() and I propose to remove thatas well; patch attached.

Do you insist on the BUG_ON?

---Subject: memcg: page_cgroup_zoneinfo never returns NULLFor a page charged to a memcg, there is always valid memcg per-zoneinfo.